In-verse, the reason each alien Ben turns into announces its name, is the Ultimatrix loading the file for the DNA sample. Ben isn't doing the announcing himself, as evidenced by his surprise when he hears the name of the alien he got.
Swampfire: Swampfire! ... was not who I was going for.
I was fine with her changing sides, to make it as if she atoned. However, Charmcaster's Heel-Face Turn is also believable in that she was distracted by her goal to reclaim her home dimension from an Evil Sorcerer (not Hex, but Ledgerdomain). Not convinced? She initially appeared with her uncle Hex, trying to reactivate magical charms that bestowed power to those who wielded them; the next time she appeared, she tried to take Ben's Omnitrix; finally, she seduced Kevin to her side and attempted to take Gwen's mana for herself. The means to those three goals? She was trying to get strong enough to face her home's usurper, and would do anything to do it, regardless of rules. However, after her second appearance, her animosity towards Ben and (especially) Gwen had grown to the point that she lost sight of her true goal and teamed up with the Tennyson team's Rogues Gallery (twice) to get back at them. Mr. Dwayne McDuffie has once again proven his great skill in Arc Welding. - Metal Shadow X
Kevin's insanity once absorbing the Ultimatrix had moments of lucidity where he is like his pre-insane self, when that didn't happen the first time he absorbed Ben's aliens. Why? Although we don't see Alien X in his monster form, Bellicus (destruction and rage) and Serena (love and compassion) are in there with him and Serena manages to win the debate only when it comes to Kevin not harming Gwen ...at first.
The main problem with that is that Alien X is locked. If he didn't get any of its powers, it's unlikely he got it's mental issues. How is he even moving if he did?
Not the OP, but Alien X was unlocked at the beginning of the episode where Kevin absorbs the Ultimatrix. It may have been re-locked when Paradox turned Ben back to normal, but it wasn't explicitly shown or stated. Besides, getting its mental issues likely came with the powers, and that's why he isn't shown to use any; Serena and Bellicus are blocking him. But since he isn't just Alien X, but has DNA from all the other Ultimatrix aliens, which explains why he's still capable of movement.
Okay, not citing when and why he was unlocked and giving a horrible explanation for why he's moving. Alien X is the only alien that has a direct effect on Ben's actions. If he would inherit anything from it it would those two personalities always warring with each other. Let's just go with the canon explanation of absorbing energy driving Osmosians insane kay? I'm willing to motion that Alien X simply chose not to be absorbed.
Ben 10,000's Ultimate Human form can use the powers of any of his aliens while still in human form. Humans are shown to pretty much be able to crossbreed with a large number of other species of aliens, so the power of Ultimate Human is to combine with the aliens in the Ultimatrix.
And speaking of that same episode, we finally get a good explaination as to how non-canon stuff like the original series what-if episode "Gwen 10" and the first live-action movie "Race Against Time" fit in the Ben 10 canon via the Multiverse theory; this also Josses the original series Ben 10,000 episodes as being Ben's canon future.
Another thing from the same episode. Eon was revealed to be an AU Ben 10,000 gone bad. In Race Against Time, he was an old man who looked nothing like Ben and had a different motivation. This makes sense when you remember his plan involved turning Ben into an Eon clone and he's been moving across the multiverse for awhile. It's easy to imagine that Eon tried again in an AU universe and succeeded, then his victim was this Eon. As for Paradox considering this Eon the same? Simple, Eon considered the Ben version himself, even saying so.
Ben 10,000's Ultimate form can use the powers of any of his aliens while still in human form. It's referred to as Ultimate Ben not Ultimate human, and it's said that the ultimate forms are created through war simulation. So if Ben where to go through a long war, he would eventually figure out how to use the powers on his own which is why Ultimate Ben 10000 can
Two things. First of all, Ben makes up his aliens' names, he doesn't use their species names. Thus, Ultimate Humungousaur is derived from a Vaxasaurian, Ultimate Cannonbolt from an Arcturan Pelarota, etc., and Ultimate Ben is indeed Ultimate human. Secondly, the war simulations are in the 1,000,000+ years range. So unless Ben's immortal, it's basically saying that, after a one-million-year species-wide civil war, humanity would evolve into something like Vilgax's Mecha-Mooks from the Ben 10: Alien Force series finale. - Classified
This also doubles as Fridge Horror but in "Prisoner 775 Is Missing", the title character has Colonel Rozem at pretty much knife point and yet lets Ultimate Wildmutt charge right at him without so much a threat. This seems like just stupidity, but then the moment Ultimate Wildmutt has him pinned down, he begs him to kill him. It suddenly becomes apparent that 775 was attempting Suicide by Cop...
At first, Kevin going from completely sane to Ax-Crazy just from absorbing energy for the first time in years doesn't quite make as much sense, but then you remember he sucked Aggregor dry. Aggregor not only fully absorbed 5 aliens, but unlike Kevin had absolutely no qualms about absorbing energy. Since for their race energy = insanity, absorbing all the energy Aggregor already had on top of Ben's aliens drove Kevin completely insane almost instantly.
On top of it, Darkstar describes his and Kevin's hunger for energy like an addiction. Kevin hadn't absorbed energy for five years. When he absorbed it again for the first time, he had a relapse into his addiction. This also explains why he went full blown Sylar this time. A relapse into an addiction often ends up being much worse than the original addition.
Actually, it seems to be because this time he absorbed some of Rath as well, so he got the reckless streak from him.
Considering she's Japanese, the 'ju' in Julie can be read as 'ten'. More fun with Theme Naming!
After thinking over what happens in "The Forge of Creation", I had a moment of Fridge Brilliance regarding something Paradox said to Ben in Alien Force: "You're much smarter now than when I first met you later". It sounds like a simple example of Time Travel Tense Trouble, but Forge of Creation actually makes sense of it! Ben would have first met Paradox in "The Forge of Creation", back when he was ten years old and temporarily displaced in time. That explains why Paradox said Ben was smarter than he was later on... he was referring to the displaced ten-year-old Ben!
In "Prisoner 775 Is Missing", we discover Colonel Rozum has been keeping aliens imprisoned for decades in horrible conditions, many for likely no good reason. The one we see has been driven insane and is suicidalto the point he breaks down and begs Ben to kill him. It's terrible to imagine what the other prisoners have gone through in the hell hole. Ben even describes the conditions in the prison as "inhuman" (Rosem's response is its because they're not human).
And then Ben happily turns into the alien's species while announcing the name Overkill to the dismay of of everyone present. Too Soon, indeed. Though Ben, being Ben, was probably just trying to lighten the mood.
At the end of the aforementioned episode, 775 attempts Suicide by Cop and having Ben kill him. Ben doesn't kill him, but 775's last seen being taken by the Plumbers. This kicks in when one realizes nothing happened to change 775's mind that he has nothing left to live for and is openly suicidal...
In "The Ultimate Enemy, part 1", Dagon turns the entire population of Earth, save the heroes and Julie (who was protected by Ship's Powered Armor) into Esoterica soldiers. Given that they all look male, 3+ billion people just got subjected to involutary Gender Bender on top of everything else.
Speaking of Dagon, anyone who's read H.P Lovecraft should know that Dagon is a pretty minor figure, not even on the same level as the Great Old Ones. If the Dagon of Ben 10 is this dangerous, then how bad is the Ben10 version of Cthulhu? Or worse, YOG-SOTHOTH?!